The present invention, in some embodiments thereof, relates to radiation detection systems used in the vicinity of pulsed radiation beams and other radiation sources; and, more particularly, but not exclusively, to x-ray and gamma-ray imaging and tracking systems used to monitor patients while they are treated by pulsed radiation therapy beams.
Radiation therapy is often used to treat cancer and other abnormal growths. Such therapy can use implanted radioactive sources (brachytherapy), or external radiation sources, generally beams, including x-ray beams and electron beams produced by linacs, as well as proton beams and heavy ion beams. Such beams are also used for radiosurgery, for example for ablating cardiac tissue to prevent atrial fibrillation. Because radiation beams can harm healthy tissue, radiation beam therapy and radiosurgery are carefully planned, with beams aimed precisely at a target such as a tumor, often with several doses of radiation given from different angles, to make sure that the target receives enough radiation, while minimizing the exposure of healthy tissue to radiation.
U.S. Pat. No. 6,683,318 to Haberer et al describes a heavy ion beam therapy system, in which positron emission tomography (PET) is used to locate radioactive nuclei that decay by positron emission, produced in the target tissue by the heavy ion beam. The PET results can verify that the heavy ion beam was aimed properly. In order to locate these positron-emitting nuclei before they have moved away from the target, PET is performed during the treatment session. The most convenient time for doing this is said to be in the time slots between beam spills, when the PET signal is less obscured by background noise than in the periods with the beam on. As defined in other publications by the inventors and their research group at Darmstadt, “beam spills” refers to periods of one to five seconds during which the beam is on, separated by time slots of similar length during which the beam is off. This use of “beam spill” is found, for example, in Parodi et al, “The Time Dependence of the γ-Ray Intensity Seen by an In-Beam PET Monitor,” downloaded from www.fzd.de/FWK/jb02/PDF/page77.pdf, on Nov. 23, 2008; Peters et al, “Spill Structure Measurements at the Heidelberg Ion Therapy Centre,” Proceedings of EPAC08, Genoa, Italy, paper TUPP127, pages 1824-1826, downloaded from epaper.kek.jp/e08/papers/tupp127.pdf, on Nov. 23, 2008; Crespo et al, “First In-Beam PET Imaging With LSO/APD Array Detectors,” IEEE Trans. Nucl. Sci. 15, 2654-2661 (2004); and Pshenichnov et al, “PET monitoring of cancer therapy with 3He and 12C beams: a study with the GEANT4 toolkit,” submitted to Phys. Med. Biol., downloaded from arxiv.org/PS_cache/arxiv/pdf/0708/0708.1691v1.pdf, on Nov. 23, 2008.
U.S. Pat. Nos. 7,438,685 and 6,804,548 describe using ultrasound to monitor the position of a target organ or tumor in real time during beam therapy. US 2005/0197564 to Dempsey describes using real time MRI during beam therapy.
U.S. Pat. No. 7,349,522 describes software for simulating dynamic radiation therapy, for example gated to respiration, using fluoroscope images fused to previously acquired reference images. But they do not suggest the use of such fluoroscope images during actual beam therapy, instead using index markers or other known methods of gating to respiration.
U.S. Pat. No. 7,302,033 describes real time “image guided radiation treatment,” using a linac for treatment, and a stereo x-ray system for real time imaging, arranged so neither one blocks the other. “Real time” is defined to mean anytime during a treatment delivery phase, with the linac turned on or off. Specifically, they describe making an x-ray image before turning on the linac, delivering a dose of radiation with the linac, then making another image with the linac turned off, delivering another dose of radiation, etc.
US 2008/0130825 to Fu et al describes using image guided radiation therapy, including x-ray imaging, while the beam is turned on or off. Image segmentation is used in real time to better identify the target, for example a tumor.
US 2005/0080332 to Shiu describes using “near simultaneous” CT image guided radiotherapy.
U.S. Pat. No. 7,295,648 describes using linac x-rays for imaging “by suitable variation of the output energy”. U.S. Pat. No. 5,233,990 describes using a lower energy therapeutic x-ray beam, from an x-ray tube, for imaging in real time, to verify the position of the patient. U.S. Pat. No. 6,839,404 describes using linac x-rays for imaging before delivering a dose of x-rays for therapy, and using the detector to monitor the dose during therapy. U.S. Pat. No. 6,618,467 describes using linac x-rays to produce CT images in real time. Because the therapy x-rays do not make up a complete set of angles for CT, they supplement them with low level x-rays at other angles, obtained from leakage through the shutters of the linac, or from sources other than the linac, collected either before or during treatment. They also describe using only the low level x-rays to produce the CT images.
U.S. Pat. No. 7,263,164 describes using an x-ray imaging system in real time, during treatment by a linac beam. Scattering from the linac beam into the detector is estimated, using a phantom, and subtracted from the image.
U.S. Pat. No. 7,171,257 describes doing x-ray imaging just before radiosurgery, finding the change in position of the beam target, for example cardiac tissue to be ablated, as a function of cardiac phase and breathing phase, then using that information, with the imaging system turned off, to keep the beam aimed correctly during the radiosurgery, monitoring the breathing and cardiac cycles in real time.
U.S. Pat. No. 6,865,411 states that it is a disadvantage that imaging and radiation beam therapy cannot be done at the same time.
U.S. Pat. No. 6,662,036 and U.S. Pat. No. 6,405,072 describe using index markers to track movement of the patient in real time, during beam therapy.
“Answer to Question #4511 Submitted to ‘Ask the Experts’” on the Health Physics Society website, downloaded on Nov. 27, 2008 from hps.org/publicinformation/ate/q4511.html, states that most medical linacs are pulsed with repetition rates of 100 to 400 pulses per second, and pulse lengths of 1 to 10 microseconds, resulting in a very low duty cycle, less than 1% or less than 0.1%, and peak intensities of radiation much higher than the average intensity. Radiation detectors that have long dead times, such as Geiger-Muller and proportional counters, tend to become saturated at such high peak intensities, and are not suitable for safety monitoring of radiation levels outside rooms where linacs are used. Similar points are made by R. McCall and N. Ipe, “The Response of Survey Meters to Pulsed Radiation Fields,” SLAC-PUB-4488 (1987), downloaded from www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-4488.pdf, on Nov. 27, 2008.
Radiation Detection and Measurement by Glenn Knoll, 3rd edition (2000), ISBN 0-471-07338-5, describes instruments for detecting x-ray and gamma-ray photons.